The present invention relates generally to systems for managing charge flow and EGR fraction in an EGR control system for an internal combustion engine, and more specifically to such systems for determining and producing desired charge flow and EGR fraction commands based on current engine operating conditions.
Systems for controlling EGR flow and/or turbocharger swallowing capacity are known and have been widely implemented, particularly in the heavy diesel engine industry. An example of one known system 10 for providing such control is shown in FIG. 1 and includes an internal combustion engine 12 having an intake manifold 14 fluidly coupled to a compressor 18 of a turbocharger 25 via intake conduit 16, wherein the compressor 18 receives fresh air via intake conduit 20. The turbocharger compressor 18 is mechanically coupled to a turbocharger turbine 24 via drive shaft 22, wherein turbine 24 is fluidly coupled to an exhaust manifold 28 of engine 12 via exhaust conduit 30, and is further fluidly coupled to ambient via exhaust conduit 26. An EGR valve 32 is disposed in fluid communication with the intake conduit 16 and the exhaust conduit 30, and a differential pressure sensor, or xcex94P sensor, 34 is disposed across the EGR valve 32 to sense a pressure change, or delta pressure, across valve 32. An electronic EGR flow controller 36 has a first input receiving a signal indicative of desired EGR valve position, and has a first output electrically connected to EGR valve 32 via signal path 38. In the system shown in FIG. 1, the EGR flow controller is configured to apply the EGR position signal directly to the EGR valve 32. Controller 36 includes a second input receiving a signal indicative of a desired delta pressure value, or xcex94P target, and a third input electrically connected to the xcex94P sensor 34 via signal path 40 and receiving a signal thereat indicative of sensed delta pressure (xcex94P). The xcex94P value is subtracted from the xcex94P target value at summing node 42, and a xcex94P error value produced thereby is applied to a proportional-integral (PI) or other known controller 44. An output of controller 44 produces a variable geometry turbocharger signal VGT that is used to control the swallowing capacity and/or efficiency of the turbocharger 25 via any of a number of known techniques via signal path 46. In operation, charge flow to the intake manifold 14 of engine 12, defined for the purposes of the present invention as the sum of fresh air flow into intake conduit 16 and EGR flow into intake conduit 16, is controlled via control of the position of the EGR valve 32 and the pressure differential between the exhaust conduit 30 and intake conduit 16.
One drawback associated with an EGR flow control system 10 of the type illustrated in FIG. 1 is that there exists an interdependency between charge flow and EGR flow such that EGR flow and fresh air flow cannot be controlled separately. Once EGR flow is established by the EGR flow controller 36, the resulting charge flow is defined by whatever fresh air flow is available. System 10 may therefore be optimized for NOx control or for particulate control, but generally not for both. It is accordingly desirable to provide for an EGR control system wherein EGR flow and fresh air flow may be controlled separately to therefore gain better and more consistent control over the charge flow. Systems for achieving this goal are described U.S. Pat. No. 6,408,834, entitled SYSTEM FOR DECOUPLING EGR FLOW AND TURBOCHARGER SWALLOWING CAPACITY/EFFICIENCY CONTROL MECHANISMS, and U.S. Pat. No. 6,480,782, entitled SYSTEM FOR MANAGING CHARGE FLOW AND EGR FRACTION IN AN INTERNAL COMBUSTION ENGINE, both of which are assigned to the assignee of the present invention and the disclosures of which are incorporated herein by reference.
In such systems, however, it is further desirable to provide target steady-state charge flow and EGR fraction commands across a wide range of operating conditions in order to optimize engine performance while also constraining engine emissions below specified limits. What is therefore needed is a control strategy operable to provide such target charge flow and EGR fraction commands to manage steady-state engine performance across a wide range of ambient and application conditions, while complying with emissions regulations that vary across those same and other conditions.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a system for producing charge flow and EGR fraction commands comprises means for determining a current ambient air density, means for determining a current operating temperature of an internal combustion engine, a memory unit having a number of data sets stored therein, each data set including a subset of charge flow and EGR fraction command values optimized for either of a unique ambient pressure and a unique engine operating temperature, and an engine controller configured to select a first one of said number of said data sets having an associated unique ambient pressure or engine operating temperature that is less than or equal to a corresponding one of said current ambient air density and said current operating temperature, and to select a second one of said number of data sets having an associated unique ambient pressure or engine operating temperature that is greater than or equal to a corresponding one of said current ambient air density and said current operating temperature, said engine controller interpolating between said first and second data sets to produce charge flow value and EGR fraction commands.
One object of the present invention is to provide a system for generating charge flow and EGR fraction commands based on one or more engine operating conditions.
Another object of the present invention is to provide such a system operable to generate such commands based on current ambient air density and/or engine temperature.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiment.